Rotary concrete saws in which the operator walks behind the saw and which are used in construction are very well known. Such self-propelled units usually are provided with the longitudinal propulsion of the unit and the rotation of the saw blade being achieved by belts connected through suitable pulley systems to a prime mover. The propulsion speed of the device and the rotational speed of the saw blade may be manually controlled by the operator. However, these units usually weigh about 1600 pounds and they are not steerable other than by sliding the wheels with handles which extend outwardly on either side of the operator. Since the cutting action of the saw blade tends to produce a drag on that side of the saw, the operator must continuously push the handle that is on the same side of the unit to attempt to keep the saw blade on the chalk line being followed in the cutting operation. With a 1600 pound unit, this is very difficult to control since the wheel positions are fixed and in the field one may observe that these handles have been heavily padded by the operator to protect his hips from being bruised by continuously pushing the handles to maintain the saw blade cutting in a straight line.
Furthermore, concrete will vary in density depending upon the ingredients used in making the concrete mix and in large area installations such as highways, airport runways, warehouse floors, etc., the density of the concrete can vary considerably from one pour to another.
In addition, in operating a concrete saw, especially in high way repair work oftentimes the saw blade will encounter reinforcing bars which must also be cut through and, of course, are far denser than concrete. In cutting through concrete, it is desirable to have the surface speed of the blade maintained at an optimum amount. The speed will vary from 9000 to 12,000 feet per minute, depending upon the diameter of the blade and the aggregate being cut.
Concrete blades used for this purpose have diamond cutting edges and are very expensive, costing about $1,200. If the blade is operated at other than optimum speed the cutting edge will wear down at a much more rapid rate, thus dramatically increasing the cost of operation.
In the devices of the prior art the surface speed of the blade and the transfer speed of the saw platform are manually controlled by the operator so that when varying densities of the material being cut are encountered, the judgment of the operator is relied upon to slow the transverse movement of the sw plateform or to modify the speed of the blade, or both, and, of course, the manner in which this is done will vary from operator to operator, depending upon their experience.
In applicant's copending patent application assigned to a common assignee, U.S. Pat. No. 4,748,966 "Self-Regulating Concrete Cutting Saw", there is disclosed an automatic feedback system for a concrete cutting saw which will vary the speed of propulsion of the platform supporting the saw, depending upon the density of the concrete being cut. Two versions of concrete cutting saws are disclosed in this patent application. One is a riding unit having two traction wheels that are driven by the same hydraulic motor and a third wheel which is used to manually steer the unit. Also disclosed is a conventional concrete cutting saw which embodies the same system of varying the speed of propulsion of the unit, depending upon the density of the concrete encounterd by the rotating saw blade, and which is steered by handles in the conventional manner described above.